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Letter
Nature 454, 81-83 (3 July 2008) | doi:10.1038/nature07068; Received 16 March 2008; Accepted 1 May 2008
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Domination of heliosheath pressure by shock-accelerated pickup ions from observations of neutral atoms
Linghua Wang1,2, Robert P. Lin1,2, Davin E. Larson2 & Janet G. Luhmann2
- Physics Department, University of California, Berkeley, California 94720-7300, USA
- Space Sciences Laboratory, University of California, Berkeley, California 94720-7450, USA
Correspondence to: Linghua Wang1,2 Correspondence and requests for materials should be addressed to L.W. (Email: windsound@ssl.berkeley.edu).
Abstract
The solar wind blows an immense magnetic bubble, the heliosphere, in the local interstellar medium (mostly neutral gas) flowing by the Sun1. Recent measurements by Voyager 2 across the termination shock, where the solar wind is slowed to subsonic speeds before entering the heliosheath, found that the shocked solar wind plasma2 contains only 
20 per cent of the energy released by the termination shock, whereas energetic particles3 above 28 keV contain only 10 per cent; 70 per cent of the energy is unaccounted for, leading to speculation2, 3 that the unmeasured pickup ions or energetic particles below 28 keV contain the missing energy. Here we report the detection and mapping of heliosheath energetic (4–20 keV) neutral atoms produced by charge exchange of suprathermal ions with interstellar neutral atoms. The energetic neutral atoms come from a source 60° wide in longitude straddling the direction of the local interstellar medium. Their energy spectra resemble those of solar wind pickup ions, but with a knee at 11 keV instead of 4 keV, indicating that their parent ions are pickup ions energized by the termination shock. These termination-shock-energized pickup ions contain the missing 70 per cent of the energy dissipated in the termination shock, and they dominate the pressure in the heliosheath.
- Physics Department, University of California, Berkeley, California 94720-7300, USA
- Space Sciences Laboratory, University of California, Berkeley, California 94720-7450, USA
Correspondence to: Linghua Wang1,2 Correspondence and requests for materials should be addressed to L.W. (Email: windsound@ssl.berkeley.edu).
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